Basic lithography process typically transfers a desired pattern from a patterned mask to the semiconductor wafer to form one or more semiconductor devices. The lithography process include an etch step, where the desired pattern is selectively etched onto the wafer. Additional etching processes may also continue to pattern the wafer or device as desired. Ideally, an etched pattern would align precisely with the etch mask to produce a zero-bias etching process. In reality, varying differences between etched patterns and mask patterns is usually present to produce a large range of etch bias. The magnitude of etch bias variation may undermine the uniformity of identical structures formed across a wafer.
There is, therefore, a need to control etch bias to achieve an optimum process window.